1. Field of the Invention
The present invention relates to a copying apparatus for forming an image of an original document placed on a platen on the surface of a copy paper sheet, and having an automatic document feeding device for feeding original documents onto a platen.
2. Description of the Related Art
Copying apparatus have been provided in recent years with automatic document feeding devices (hereinafter referred to as "ADF") to decrease the manual labor of exchanging original documents and increase copy processing capacity. The ADF feeds original documents one sheet at a time and places the fed sheet at a predetermined position on a glass platen, then discharges the scanned original document from the glass platen.
The ADF allows high-speed copy processing by prefeeding a next original document into the original feed path immediately after feeding a prior original document (hereinafter referred to as "prefeed process").
In conventional copying apparatus, however, the paper prefeed process is only executed for the second sheet. Therefore, even when there is suitable space available to allow a prefeed process for a third sheet due to a relatively long feed path extending from the feed opening to immediately in front of the image transfer portion, a prefeed process for a third sheet cannot be implemented, thereby preventing a subsequent increase in copy speed.
Conventional ADF separately provide a motor for driving a feed means for feeding original documents from the paper tray to immediately in front of the glass platen, and a motor for driving a transport means for transporting the original document onto the glass platen. In recent years, there has been strong demand for higher speed copy processing using ADF, and the percentage of mid-grade apparatus and basic-grade apparatus incorporating ADF has increased.
It is, however, extremely difficult to reduce the cost of conventional copying apparatus which use separate motors to independently drive the paper feed means and the paper transport means.